Optical scanning devices, which are also referred to as “pick-ups” and are a component of appliances for recording and/or for reproduction of information or data in or from one or more recording tracks on an optical storage medium, are known, for example, from EP 0 365 070. Appliances having a scanning device such as this are found in EP 1 014 349.
The respective scanning device is normally arranged on a carriage, which can be moved obliquely with respect to or at right angles to the recording track and is guided on at least one guide rod, or is designed to form such a carriage, and is connected to an electric-motor drive in order to achieve a high speed and high positioning accuracy, associated with a short access time to different points on the storage medium. In the appliance which is described in EP 1 014 349, the scanning device is attached by means of holding elements to a guide rod and to a drive shaft, which is driven by an electric motor. However, the carriage may also be coupled to a toothed rod which is driven by an electric motor via a gear wheel transmission. The guide rail and the drive shaft, and/or the toothed rod, as well as the electric motor are attached to a base plate, to which a disc motor is also attached, which drives a turntable for an optical storage medium. Guide blocks for linear movement of the guide rod are arranged on the carriage, and guide holes and/or sliding holes are incorporated in them.
Sliding bearings which may be based on different design principles are frequently arranged or formed in order to improve the sliding characteristics of the scanning device. Since the scanning device together with its components for guidance and alignment of a laser beam and their association with one another determines the so-called optical path, that is to say the path to the respective recording medium, it is helpful for not only the components of the scanning device to be adjustable, but also for them to be adjustable as a unit with respect to the optical storage medium.
In addition to the capability to adjust the sliding bearings on the guide rod or rods with piezoelectric elements and spring means arranged in the sliding bearings, and thus to determine the radial position and the inclination of the respective sliding bearing with respect to the guide rod, as is the case with the scanning device described in JP-2001-357553, it is also possible to use sliding bearing bushes. For this purpose, JP-62-001127 describes a carriage arrangement with a bearing block (guide block) with two sliding bearing bushes which are separated from one another, are on the same axis and are arranged on a guide rod, in which case the common axis of the sliding bearing bushes may also be inclined with respect to the guide block. The sliding bearing bushes are adjusted with respect to the guide rod by movement of the entire guide block.
The sliding bearing bushes are normally pushed into or else adhesively bonded in the holes. Because of the required positioning accuracy for the scanning device, the diameters of the sliding bearings, their parallelity with respect to the guide axis and their coaxiality must be very accurate. In this case, tolerance problems and concentricity problems may occur between the two holes for the sliding bearing bushes, and these problems are transferred to the sliding bearing bushes. Furthermore, the process of pushing them in may reduce their very accurate internal diameter, thus adversely affecting their capability to slide on the guide rod.